This invention relates to coated articles that have approximately the same color characteristics as viewed by the naked eye before and after heat treatment (e.g., thermal tempering), and corresponding methods. Such coated articles may be used in insulating glass (IG) units, vehicle windows, and/or other suitable applications.
The need for color matchability of coated articles (before heat treatment vs. after heat treatment) is known. Glass substrates are often produced in large quantities and cut to size in order to fulfill the needs of a particular situation such as a new multi-window and door office building, vehicle window needs, etc. It is often desirable in such applications that some of the windows and/or doors be heat-treated (i.e., tempered, heat strengthened or bent), while others need not be. Office buildings often employ IG units and/or laminates for safety and/or thermal control. It is often desirable that the units and/or laminates which are heat treated (HT) substantially match their non-heat treated counterparts (e.g., with regard to color, reflectance, and/or the like) for architectural and/or aesthetic purposes.
U.S. Pat. No. 5,376,455 discloses a coated article including: glass/Si3N4/NiCr/Ag/NiCr/Si3N4. Unfortunately, the coating system of the ""455 patent is not sufficiently color matchable after heat treatment with its non-heat-treated counterpart. In other words, the coating system of the ""455 patent has a rather high xcex94E value. This means that, unfortunately, two different coated articles with different coatings (one to be heat treated, the other not to be) must be made for customers who want their heat-treated and non-heat-treated coated articles to approximately match colorwise as viewed by the naked eye.
As with the ""455 patent, it has mostly been possible to achieve matchability only by providing two different layer systems, one of which is heat treated (HT) and the other is not. The necessity of developing and using two different layer systems to achieve matchability creates additional manufacturing expense and inventory needs which are undesirable.
However, commonly owned U.S. Pat. No. 5,688,585 discloses a solar control coated article including glass/Si3N4/NiCr/Si3N4, wherein matchability is achieved with a single layer system. An object of the ""585 patent is to provide a sputter coated layer system that after heat treatment is matchable colorwise with its non-heat-treated counterpart. However, the ""585 patent uses a heat treatment (HT) of only three (3) minutes (col. 10, line 55). Longer heat treatments are often desired in order to attain better tempering or HT characteristics. Unfortunately, as explained below, it has been found that with longer HT times the coatings of the ""585 patent cannot maintain low xcex94E values and thus lose color matchability. In particular, it has been found that in coatings such as those of the ""585 patent, xcex94E values jump significantly upward after HT for 4-5 minutes at a temperature of from about 600 to 800 degrees C.
Referring to FIG. 1, consider the following layer stack (see Comparative Example below): glass/Si3N4/NiCr/Si3N4, where the underlayer of Si3N4 is about 50-70 xc3x85 (angstroms) thick, the NiCr layer is about 325 xc3x85 thick, and the overcoat of Si3N4 is about 210-310 xc3x85 thick. As explained in the Comparative Example below, this coated article has a rather high transmissive xcex94E* value of about 5.9 after heat treatment (HT) at 625 degrees C. for ten (10) minutes. This high transmissive xcex94E value means that a HT version of the ""585 coated article does not approximately match colorwise non-heat-treated counterpart versions with regard to transmissive color after 10 minutes of HT. This is not desirable.
The following Comparative Example coated article (ultimately annealed and heat treated) was made as shown in FIG. 1. The layer system xe2x80x9cLxe2x80x9d, as shown in FIG. 1, was provided on about 6.0 mm thick clear soda-lime-silica glass substrate 1, and was: silicon nitride/NiCr/silicon nitride. A Leybold Terra-G six-chamber sputter coating apparatus was used to sputter the coating onto the glass substrate. Five cathodes were in each chamber, so there were a total of 30 cathode targets in the sputter coater (not all were used). Cathode numbering utilizes the first digit to refer to the coater chamber, and the second digit to refer to the cathode position in that chamber. For example, cathode #42 was the second cathode (second digit) in the fourth (first digit) sputter chamber. Cathode #s 42, 55 and 61 were dual C-Mag type cathodes; and cathode #s 44 and 45 were planar cathodes. Below, xe2x80x9c*xe2x80x9d means Al content of approximately 10%. The line speed was 3.5 meters per minute (m/min.). All gas flows (e.g., Ar and N) are presented in units of sccm. Voltage is measured in terms of volts, and frequency in terms of kHz. Pressure is measured in hPa, and power in kW. T-gas refers to trim gas used to individually adjust gas flows along cathode length to make corrections regarding layer thickness uniformity (all T-gas was at 100 sccm). C % refers to the percentage (%) of trim gas introduced at the center, while PS % refers to the percentage of the trim gas introduced at the pump side, and VS % refers to the percentage of the trim or tuning gas introduced at the viewer side. The NiCr targets were approximately 80/20 NiCr.
After being sputtered onto glass substrate 1 as set forth above, the resulting coated article of the Comparative Example was tested and found to have the following characteristics monolithically (not in an IG unit), where the heat treatment (HT) involved heating the monolithic product at about 625 degrees C. for about 10 minutes. It is noted that a* and b* color coordinate values are in accordance with CIE LAB 1976, Ill. C 2 degree observer technique, and xcex94a* and xcex94b* are in terms of absolute value. Moreover, sheet resistance (Rs) is in units of ohms per square as is known in the art.
As can be seen above, the Comparative Example experienced a rather high transmissive xcex94E* value of 5.9 (evidencing that the coating is not color stable upon HT). It is believed that the high xcex94E* value associated with the coating of the Comparative Example is caused for at least the following reasons.
FIG. 2 is an XPS plot illustrating the Comparative Example coating before heat treatment (HT), while FIG. 3 illustrates the Comparative Example coating after HT. As shown in FIG. 2, before heat treatment the three different layers are fairly separate and distinct. For example, prior to HT it can be seen that the Ni slopes 3 on either side of the NiCr layer are very steep, as are the Si and N slopes 5 and 7, respectively, on the lower side of the upper (i.e., overcoat) Si3N4 layer. Therefore, prior to HT, the vast majority of the Ni is located in the NiCr layer and the vast majority of the Si and N from the upper Si3N4 layer is located in that layer.
However, FIG. 3 illustrates that when the Comparative Example coated article is heat treated (HT) for 10 minutes as discussed above, a significant portion of the Ni from the NiCr layer migrates (of diffuses) into the upper Si3N4 layer. Additionally, upon HT a significant portion of the Si and N from the upper Si3N4 layer migrate(s) into the NiCr layer. In other words, the interface between the metal NiCr layer and the upper dielectric Si3N4 layer becomes blurred and non-distinct. This is evidenced in FIG. 3 by the less steep slope 3a of the Ni on the upper/outer side of the NiCr layer, and by the less steep slopes 5a and 7a of the Si and N on the lower side of the upper Si3N4 layer (relative to the slopes in FIG. 2).
Unfortunately, the aforesaid migrations of the Si, N, and Ni from their FIG. 2 positions to their respective FIG. 3 positions due to HT causes significant color shifting to occur and thus explains the large transmissive xcex94E* value associated with the Comparative Example.
In view of the above, it will be apparent to those skilled in the art that there exists a need for a coating or layer system that has a low xcex94E (or xcex94E*) value(s) (transmissive and/or glass side reflective) and thus good color matchability characteristics after at least five (5) minutes of heat treatment (HT). It is a purpose of this invention to fulfill the above-listed need, and/or other needs which will become more apparent to the skilled artisan once given the following disclosure.
An object of this invention is to provide a coating or layer system that has good color stability (i.e., a low xcex94E* value(s)) with heat treatment (HT).
Another object of this invention is to provide a coating or layer system having a xcex94E* value (transmissive and/or glass side reflective) no greater than 5.0 (more preferably no greater than 4.0, and most preferably no greater than 3.0) upon heat treatment (HT) at a temperature of at least about 600 degrees C. for a period of time of at least 5 minutes (more preferably at least 7 minutes, and most preferably at least 9 minutes).
Another object of this invention is to provide a diffusion/migration prevention layer (i.e., anti-migration layer) between a dielectric layer (e.g., SixNY) and a solar control layer (e.g., NiCr) in order to reduce elemental migration and improve color stability upon HT so as to enable the resulting coated article to have the aforesaid low xcex94E value(s). The anti-migration layer may include chromium oxide, NiCrOx, or any other suitable material such as another metal oxide.
Another object of this invention is to fulfill one or more of the above-listed objects.
According to certain example embodiments of this invention, by at least positioning an anti-migration layer between a solar control layer and a dielectric layer, migration of N, Cr, and/or Ni (or other relevant material(s) depending upon the materials used for the dielectric and solar control layers) can be reduced during HT thereby enabling the resulting coated article to be more color-stable with HT (i.e., have lower xcex94E* value(s)). Less element migration during HT results in better color stability upon HT, and thus lower xcex94E* value(s). It has also been found that the provision of anti-migration layer(s) may improve the chemical durability of coatings herein (e.g., improve corrosion resistance of the coating) in some example embodiments.
Generally speaking, certain example embodiments of this invention fulfill one or more of the above-listed objects or needs by providing a coated article comprising:
a layer system supported by a glass substrate, said layer system comprising an IR (infrared) reflecting layer located between first and second dielectric layers, wherein the second dielectric layer is at least partially nitrided and positioned so that the IR reflecting layer is between the second dielectric layer and the glass substrate; and
an anti-migration layer comprising chromium oxide located between said IR reflecting layer and said second dielectric layer so that the coated article has a transmissive xcex94E*T value no greater than 5.0 after heat treatment at a temperature of at least about 600 degrees C.
Certain other example embodiments of this invention fulfill one or more of the above-listed objects by providing a coated article comprising:
a glass substrate; and
a layer system supported by said substrate, said layer system including a metal oxide inclusive layer located between a metal or metal nitride layer and a dielectric layer so that the coated article has a xcex94E* value no greater than 5.0 after thermal tempering or heat bending.
Still further example embodiments of this invention fulfill one or more of the above-listed objects or needs by providing a method of making a coated article, the method comprising:
depositing a metal layer on a substrate;
depositing a metal oxide layer on the substrate over the metal layer;
depositing a dielectric layer on the substrate over the metal layer and over the metal oxide layer; and
heat treating the article comprising the above-listed deposited layers at a temperature of at least about 600 degrees C. so that after said heat treating the coated article has a xcex94E* value no greater than 5.0.
This invention will now be described with respect to certain embodiments thereof as illustrated in the following drawings, wherein: